1. Field of the Invention
The present invention relates to an evaluation method for evaluating a coating sag and a coating control system utilizing the evaluation method.
2. Related Art
In the field of automotive industry utilizing various kinds of robots, various problems concerning the robots have recently been produced. For example, the structure and function of the robot have become complicated so that it is difficult to design a robot of a desirable structure and function. Teaching the robots is also complicated and takes long considering that a number of robots are employed and that kinds or variations of vehicles are increased.
In order to deal with the above problems, a robot simulation system utilizing CAD (computer aided design), in which a teaching operation is performed by means of a computer simulation, is expected. In case of a coating robot among the various robots, it is important to control not only a coating line of coating gun on a work to be coated but also coating conditions, such as a discharge amount of the coating material, coating speed and the like. Therefore, it is necessary for a robot teaching system according to the computer simulation to perform the teaching of such coating conditions appropriately.
Meanwhile, when introducing a robot into a manufacturing line of the automotive vehicles, it is necessary to design how the robot is operated. In other words, it is necessary to make a teaching of the robot operation in advance. The design or teaching of the robot operation is to first determine a series of tasks to be done by the robot, then determine details of each of the tasks, such as layout of the robot, tool for the robot, operation order to be done by the robot, peripheral installment of the robot and the like evaluating attitude, such as three dimensional position orientation of the robot, and operation efficiency (such as operation cycle, moving distance of the robot and the like).
At this stage of the design or basic teaching of the robot operation, an actual robot and work or object to which the robot is applied are not used. Therefore, a robot designer is required to design the robot operation or movement based on his three dimensional imagination. This conventional way of the robot design or teaching, however, often results in inconvenient or deficient robot performance due to the uncertainty during the design work of the robot.
In order to solve the above problem, it is preferable to introduce a teaching play back system for teaching the robot. In the proposed teaching play back system, which is a so called direct teaching play back system, the robot teaching is directly applied on an actual robot operating actually the robot using an actual work. However, this system is time consuming and costly.
In order to deal with such problems, recently it is proposed to introduce a computer simulation method for designing the robot operation (CAD simulation). The CAD simulation is to perform teaching a robot utilizing a computer simulation system, instead of utilizing the direct teaching play back system in which each robot is directly subjected to a teaching. In the CAD simulation system, a robot, jig, peripheral installments and the like are displayed on a screen of CAD system so that the teaching is performed through a computer simulation on the screen. The teaching data obtained through the CAD simulation is loaded down on an actual robot to be operated properly.
The CAD simulation is further explained with regard to a robot in the field of the automotive industry.
First, working data are determined. The working data includes all information concerning a robot operation, such as configuration of work, kind of work such as body, bumper, information concerning coating gun, jig and the like. Then, teaching data for a robot are determined through a computer simulation which is performed based on the working data. The resultant teaching data are examined if there is a contradiction between the data, or if the operation cycle time is suitable with an automatic simulation mode of the computer. When the teaching data are held appropriate, the teaching data are converted to a machine language and loaded down on an actual robot. The robot is operated in accordance with the teaching result.
The above mentioned CAD simulation works out for a specific kind of robots such as a welding robot as far as a position, speed, moving line of the robot and the like are properly provided, since objects of those kinds of robots can be accomplished merely by controlling the movement of the robots.
On the contrary, in a case of a coating robot as disclosed in Japanese Patent Public Disclosure No. 2-280865, it is important to control not only the movement of the robot but also coating conditions or coating variables for determining a coating thickness. Thus, in this type of robot, mere moving line control of the robot is not enough to obtain a desirable performance. The coating conditions include, in particular, a discharging amount of a coating material, coating electrostatic voltage, atomization pressure of the coating material and the like.
Conventionally, the coating conditions are determined through the direct teaching play back system using the actual robot even though the teaching of the robot movement is performed by means of the CAD simulation. The teaching of the coating robot according to the direct teaching play back system is made so as to determine a coating line to be taken by a coating gun based on a shape, position of a vehicle body and the like to be coated. Then, the coating line data is stored in a memory of a control unit. A number of teaching points are provided on the determined coating line of the robot. A coating speed, delivery amount of the coating material, a discharging direction of the coating material and the like concerning the respective teaching points are determined and data providing the above coating conditions are stored in a memory. In addition, robot operation data are formed on the coating robot for moving the coating gun in accordance with the coating line data, operation data. Then, a control program including the coating condition data and operation data for the coating robot is finally determined.
After teaching, the coating robot is operated in accordance with the control program which is provided by the control unit. The coating robot moves the coating gun along the coating line determined and controls the coating gun to make a coating action of a vehicle body in accordance with the determined coating conditions, which include the coating speed, coating amount, coating direction and the like.
It should, however, be noted that the conventional robot teaching in determining the coating conditions or coating variables according to the direct play back teaching is needed to provide a number of teaching points and therefore increase the number of steps to be done. In addition, since the actual coating robot and the actual work, such as vehicle body to be coated, have to be used for performing the teaching action, the time for the teaching action is quite restricted. Therefore, it is difficult to obtain an optimized control program for the robot. In order to deal with the above problems, it is also proposed that a computer simulation to be introduced to perform the teaching of the coating conditions (simulation teaching play back) in order to eliminate such actual use of the coating robot and work.
However, it is difficult to determine desirable coating conditions of the coating robot through the conventional CAD simulation even if a number of teaching points are provided for getting data of the coating conditions, such as coating speed, coating amount, discharging direction of the coating material and the like. This is because the coating conditions conventionally determined through the CAD simulation is not enough to control the performance of a coating robot.
In view of this, it is proposed that a coating efficiency on a work or object to be coated is calculated in addition to the conventional coating conditions at the respective teaching points and that the coating efficiency to be taken into account in performing the teaching of a coating, robot.
The coating efficiency means a ratio of an amount of a coating material forming a coating actually deposited on a coating surface to be coated to that of the coating material discharged toward the coating surface from the coating gun. The coating efficiency can be obtained by a multiple regression analysis method utilizing a coating material atomization pressure and coating electrostatic voltage as control variables or further including a discharging amount of the coating material from the coating gun and a distance between the gun and the coating surface in addition to the atomization pressure and electrostatic voltage as control variables. The above coating deposited on the coating surface means a coating layer which is discharged on the coating surface and dried and shrunk.
Accordingly, the control variables determined based on both the input variable data and the coating efficiency are reliable to control the robot performance so that the control program in accordance with the control variables determined by means of the above teaching method provides a desirable coating.
It should, however, be noted that although the above method can provide a desirable result in a case of a flat coating surface, it is not well applicable to a coating surface of a work having an undulation or unevenness, such as engine room, trunk room of an automotive vehicle or if the coating surface is inclined since it is difficult to provide accurate control variables. In other words, the above method is disadvantageous in that if there is an inclination, undulation or unevenness in the coating surface, it is difficult to provide a uniform thickness of coating.
Further, if the coating surface is inclined with regard to the orientation of the gun, or with regard to the vertical direction, the coating thickness varies from place to place. Otherwise, a sagging of coating is undesirably produced.